By replacing the balloon with a stationary tube
or container and filling the tube with air from a
fan or series of fans, we can use the discharge air
to do work by turning a fan at the rear of the tube
(fig. 6-7, view A).
If fuel is added and combustion occurs, we
greatly increase both the volume of air and the
velocity that propels it over the fan. This increases
the horsepower the fan will produce (fig. 6-7, view
B). The continuous pressure created by the inlet
fan, or compressor, prevents the hot gases from
going forward.
Next, if we attach a shaft to the compressor
and extend it back to a turbine wheel, we have
a simple gas turbine. It can supply power to run
its own compressor and still provide enough
power to do useful work, such as to drive a
generator or propel a ship (fig. 6-8, view A).
By comparing view A with view B in figure
6-8, you can see that a gas turbine is very similar
to our balloon turbine.
THEORETICAL CYCLES
A cycle is a process that begins with certain
conditions, progresses through a series of events,
and returns to the original conditions.
As an introduction to gas turbine operation,
consider first the reciprocating engine, which
operates on the Otto cycle. (fig, 6-9, view A).
The Otto cycle consists of four basic events that
occur at different times but in the same place,
Figure 6-9.—A comparison of reciprocating and gas turbine engine cycles.
6-5
